chain vs. gear drive

[flyinlow]

So you sit there watching the timing at idle dancing around 3,4,5 degrees +or -  . Better at 3000 rpm. Where's the slop?  chain? cam/intermediate shaft?  Distributor shaft tang to slot?

Does a gear drive get rid of this?

[Eldovert]

Usually the chain...you can measure the slop by rotating the crank by hand with the distributor cap off...as soon as the rotor moves,rotate the crank in the opposite direction until it moves again...you can measure the degrees of slack on the damper.
A good name brand chain is good enough for the street IMO.

[Challenger340]

If it's a really old engine with a sloppy chain I guess that could cause the spark could jump around a bit ?
however...
if you see the spark jumping around on a fresh build with a tight chain ? it's typically what's referenced as "spark scatter".... and caused by other issues within the ignition system ie: Hall effect resistance/inconsistency

[Kern Dog]

The story that I read was that with some Mopar Performance distributors, the internal parts include really small and light advance weights that are too light to be stable. They flutter around and cause the timing to vary a LOT.